The present invention is directed to an adapter for operating a keyhole saw on a driving machine, in particular an electric hand-held drill.
A known part of an adapter which forms a “power change system” for receiving a keyhole saw (EP 1 193 014 A1 and DE 601 04 177 T2) has the shape of a hollow hexagonal prism which is provided, at one end, with a threaded section around its circumference, and, close to the other end, it is provided with a circumferential, concave detent groove. The threaded section is screwed into a central threaded hole of the keyhole saw, and the adapter—having the keyhole saw attached thereto—is slid via its hexagonal prism into a drive sleeve having an inner, hexagonal sleeve wall until a detent ball which is held in a radial bore in the sleeve wall drops into the detent groove and holds the adapter in a non-displaceable manner. A sliding sleeve which is displaceable against the restoring force of a compression spring is situated on the drive sleeve for locking and unlocking the adapter. In the locking position, the sliding sleeve closes the radial bore to the outside, thereby blocking the detent ball which has dropped into the detent groove of the adapter and preventing it from being displaced in the radial direction. In the unlocking position, which the sliding sleeve assumes after following a displacement path against the restoring force of the compression spring, the radial bore is congruent with a recess in the inner wall of the sliding sleeve, thereby allowing the detent ball to escape radially outwardly when one of the groove flanks of the detent groove in the adapter strikes the detent ball when the adapter is pulled out of the drive sleeve, or when the adapter is slid into the drive sleeve. The drive sleeve includes a hexagonal receiving shank which is placed in the chuck of an electric hand-held power tool. When drilling is performed using the keyhole saw, a “pilot bit” is typically used to guide the keyhole saw in an exact manner. The pilot bit includes a hexagonal shank and a circumferential detent groove in the hexagonal shank, and it is held in a bit-connecting piece in a non-rotatable manner via the hexagonal shank and via a detent ball which drops into the detent groove in the hexagonal shank of the pilot bit, the detent ball being held in an axially non-displaceable manner in the bit-connecting piece in a radial bore. The bit-connecting piece is accommodated in the adapter and extends via a hexagonal segment part into the similarly formed hollow interior of the shank of the drive sleeve.
Given large diameters of the keyhole saw, to prevent the thread from stripping when high torques are transferred, two diametrically opposed driving holes are provided in the keyhole saw, and two axially extending driving pegs which extend into the driving holes are situated on the end face—which faces the keyhole saw—of the drive sleeve. The transfer of torque from the electric hand-held power tool via the drive sleeve to the keyhole saw therefore takes place via the driving pegs and the driving holes, and the load is relieved from the threaded connection between the keyhole saw and the adapter. The connection between the keyhole saw and the electric hand-held power tool is established by screwing the adapter via its threaded section tightly into the threaded hole of the keyhole saw, and then inserting the adapter into the drive sleeve until the driving pegs strike the keyhole saw. After the driving pegs are aligned with the driving holes, the adapter is slid completely into the drive sleeve, and the driving pegs enter the driving holes; the sliding sleeve must be pushed back against the force of the restoring spring until the detent groove of the adapter moves under the detent ball, then the detent ball drops into the detent groove. After the sliding sleeve is released, the restoring spring forces the sliding sleeve back, and the adapter is locked in place in the drive sleeve in an axially non-displaceable manner. After the pilot bit is inserted, the drive sleeve is inserted via its hexagonal shank into the chuck of the electric hand-held drill.
In the case of a known adapter, which is of a “standard design” and may be inserted directly into the chuck of an electric hand-held power tool, the driving pegs and threaded section are also situated on two separate components which are placed on the keyhole saw individually, while being joined together, and are then detachably connected to one another. The hollow component which includes the threaded section, into which the pilot bit is also inserted, includes a hexagonal clamping shank which is inserted into the chuck of the electric hand-held power tool, while the component on which the driving pegs are mounted is attached via a radial screw to the threaded section and the component on which the clamping shank is mounted.